1. Field of the Invention
The present invention relates to a piezoelectric actuator unit and a method for testing piezoelectric actuator unit, and more elaborately, to a piezoelectric actuator unit having a structure in which a connection between a piezoelectric actuator and a wiring board is reinforced by a reinforcing contact point, and a method for testing a connection of a reinforcing contact point which reinforces the connection between the piezoelectric actuator and the wiring board.
2. Description of the Related Art
In US Patent Application Publication No. 2006/0170738 (corresponds to Japanese Patent Application Laid-open No. 2006-231913), an ink-jet head which includes a piezoelectric actuator has been disclosed. The piezoelectric actuator shown in diagrams such as FIG. 4 of US Patent Application Publication No. 2006/0170738 includes a plurality of piezoelectric layers (piezoelectric sheets) stacked in a direction of thickness, a plurality of individual electrodes arranged on one surface of each of the piezoelectric layers, and Common electrodes which are arranged on the other surfaces of the piezoelectric layers, facing the plurality of individual electrodes, sandwiching the piezoelectric layers therebetween. A constraining sheet is stacked on an upper surface of the uppermost piezoelectric layer, and furthermore, a top sheet is stacked on an upper surface of the constraining sheet. Moreover, a large number of contact points (connecting terminals) which are in conduction with the individual electrodes and the common electrodes are formed on an upper surface of the piezoelectric actuator (an upper surface of the top sheet). The contact points are connected to a large number of substrate-side electrodes respectively, of a flexible printed circuit board (FPC) which is arranged to cover the upper surface of the piezoelectric actuator by solder. A signal which has been outputted from an IC mounted on the FPC is transmitted to wires on the FPC, and the individual electrodes and the common electrodes via the contact points connected to the FPC.
Moreover, in FIG. 10 of US Patent Application Publication No. 2006/0170738, an embodiment, in which reinforcing contact points which do not contribute to transmission of signals are provided on the upper surface of the piezoelectric actuator separately from the contact points which are in conduction with the individual electrodes and the common electrodes, has been disclosed. These reinforcing contact points, similar to the large number of contact points, are connected to electrodes (dummy electrodes which are not connected to the IC) provided on an FPC side by solder. A joining strength of the piezoelectric actuator and the FPC is improved by these reinforcing contact points, and the FPC is hardly exfoliated.
Defects of connections between the contact points for signal transmission of the piezoelectric actuator and the FPC are directly related to defects of signal transmission, and eventually, to defects of operation of the piezoelectric actuator. Therefore, regarding these contact points, non-destructive testing of connection of all the contact points and the FPC has hitherto been carried out generally by detecting the conduction electrically. However, since the reinforcing contact points which reinforce the joining of the piezoelectric actuator and the FPC are not for the purpose of signal transmission, the connection could not be tested by the non-destructive testing similar to the contact points for the signal transmission described above.
However, when the reinforcing contact points have been provided, the joint strength between the piezoelectric actuator and the FPC is designed on the assumption that these reinforcing contact points are provided. Accordingly, even for the reinforcing contact points, the testing of the connection with the FPC has been sought strongly.